A rotary-piston machine whose principle is disclosed by DE No. 2,603,462 C3 is suitable for supercharging an internal combustion engine, since it is distinguished by a virtually pulsation-free delivery of the working medium, consisting, for example, of air or an air-fuel mixture. During the operation of a supercharging device of this type, a plurality of crescent-shaped working spaces are enclosed along the delivery space between the displacer and the two peripheral walls of the delivery space, which working spaces move from the inlet through the delivery space to the outlet. At the same time, its volume is increasingly reduced with a corresponding increase in the pressure of the working medium. The seal between the working spaces above and below the displacer is of crucial importance here.
U.S. Pat. No. 3,994,636 discloses a displacement machine of the type mentioned at the beginning. In order to achieve an effective radial seal between the end faces of the displacer and the side walls of the delivery space, effective axial contact is to be made between the two elements. For this purpose, the displacer, at its end face, is provided with a groove which is a seat for a sealing strip inserted therein. This sealing strip is made of an elastic, slideable material and is dimensioned in such a way that it can be moved axially and slightly radially inside the groove. A force-exerting spring element, which is a metallic spring band having a U-shaped cross section, is placed underneath.
In small spiral superchargers, however, the configuration of the groove is restricted. If, for example, the displacer only has an overall thickness of 4 mm, the groove width can be 2 mm at most. In this case, the said embodiment has two drawbacks: on the one hand, the spring element, if it is to extend over the entire groove length or sealing length, must be pre-bent mechanically in order to match the spiral-shaped profile of the groove; on the other hand, the spring deflection achievable is exceptionally small, as revealed, incidentally, by FIG. 8 of the said publication; on account of the spring characteristic, this has an unfavorable effect on the constancy of the contact pressure.
From the same publication it is known to achieve greater spring displacements by the use of helical springs, of which a certain number sit in corresponding bores in the groove in such a way as to be distributed uniformly over the sealing length (FIGS. 5, 6 of U.S. Pat. No. 3,994,636). However, this solution makes the manufacture of the displacer more expensive and complicates, not insignificantly, the assembly of the super-charger device.
It is also known from the same U.S. Pat. No. 3,994,636 to use rubber cords as spring-elastic means. However, round cords of this type have the disadvantage that they have a relatively flat spring characteristic, ie. they are relatively rigid. They are able to compensate for the tolerances occurring during production and assembly of the machine only to a limited degree. In addition, they tend to change spring properties or even completely lose them as a result of setting phenomena occurring during the operating period.